Pirates Of The Caribbean's Ian McShane and Homeland star David Harewood have also been signed up for the Bond-inspired comedy, according to The Hollywood Reporter.
Grimsby - co-written and produced by Baron Cohen - sees the Ali G star play a reformed football hooligan forced to go on the run with his brother - a suave secret agent played by Mark Strong.
The film is being made by Louis Leterrier, who directed Baron Cohen's wife Isla Fisher in illusionist crime thriller Now You See Me.
The roles for the new cast members have not been revealed at this stage.
While comic Vegas has appeared in several BBC sitcoms and in modest British films such as Kinky Boots and The Harry Hill Movie, this will be his first role in a big budget production.
Fellow Brit McShane will also be seen in Brett Ratner's Hercules opposite Dwayne 'The Rock' Johnson, while Harewood is due to appear in films SuperBob and Free In Deed, following his departure from hit drama Homeland.
Sidibe - currently the only US cast member confirmed - rose to fame for her Oscar-nominated performance in 2009's Precious and most recently appeared in TV show American Horror Story.